Intramolekulare Beweglichkeit eines Dibenzo-[b,f]-1,4-thiazepin-5-oxids. 13. Mitteilung über siebengliedrige Heterocyclen

The kinetics of the equilibrium in aqueous solution between the diasteromers of 2-Chloro-11-(4-methyl-1-piperazinyl-4-oxide)-dibenzo-[b, f]-1,4-thiazepine-5-oxide (V) have been investigated. Both isomers differ in the position of the oxygen atom of the sulphoxide group. The sulphoxide group. The isomer with a pseudo-equatorial oxygen atom is 0.75 kcal/mol more stable than the isomer with the pseudo-axial oxygen atom. The calculated free energies of activation δG≠ are 24.6 kcal/mol and 23.9 kcal/mol.     

Deoxy-nitrosugars. 5th Communication. The anomeric effect of the nitro group

The 1-deoxy-1-nitro-D -manno-pyranose 4 was transformed into the nitroolefin 5 and hence into the anomeric 1,2-dideoxy-1-nitro-3, 4, 6-tri-O-benzyl-D -arabino-hexopyranoses ( 3a and 3b ; cf. the Scheme). Conformational analysis of 1-benzyloxy-2-nitroethane ( 6 ) by ¹H-NMR spectroscopy (Fig. 2) showed the synclinal conformation to be more stable than the antiperiplanar one by about 1.4 kcal/mol (attractive gauche-effect). This gauche-effect favours the 1-deoxy-1-nitro-2, 3, 4, 6-tetra-O-benzyl-β-D -manno-hexopyranose ( 1b ) possessing an equatorial nitro group, which is, however, qualitatively the less stable anomer. The relative concentrations of the anomers of 1 and 3 , respectively, were determined by ¹H-NMR spectroscopy after base catalyzed equilibration at 37° in CHCl₃-solution (Table). Anomeric effects for the nitro group of approximately 2.4 kcal/mol in 3 and of approximately 3.4 kcal/mol in 1 were calculated.     

Theoretical study on structures and stability of triplet SiC<Subscript>3</Subscript>O isomers

Various levels of calculations are carried out~for exploring the potential energy surface (PES) of triplet SiC₃O, a molecule of potential interest in interstellar chemistry. A total of 38 isomers are located on the PES including chain-like, cyclic and cage-like structures, which are connected by 87 interconversion transition states at the DFT/B3LYP/6-311G(d) level. The structures of the most relevant isomers and transition states are further optimized at the QCISD/6-311G(d) level followed by CCSD(T)/6-311+G(2df) single-point energy calculations. At the QCISD level, the lowest lying isomer is a linear SiCCCO 1 (0.0 kcal/mol) with the ³ ∑ electronic state, which possesses great kinetic stability of 59.5 kcal/mol and predominant resonant structure . In addition, the bent isomers CSiCCO 2 (68.3 kcal/mol) and OSiCCC 5 (60.1 kcal/mol) with considerable kinetic stability are also predicted to be candidates for future experimental and astrophysical detection. The bond natures and possible formation pathways in interstellar space of the three stable isomers are discussed. The predicted structures and spectroscopic properties for the relevant isomers are expected to be informative for the identification of SiC₃O and even larger SiC _n O species in laboratory and interstellar medium. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Theoretical predictions of the structure, gas-phase acidity and aromaticity of 1,2-diseleno-3,4-dithiosquaric acid

Results of ab initio self-consistent-field (SCF) and density functional theory (DFT) calculations of the gas-phase structure, acidity (free energy of deprotonation, ΔG^o), and aromaticity of 1,2-diseleno-3,4-dithiosquaric acid (3,4-dithiohydroxy-3-cyclobutene-1,2-diselenone, H₂C₄Se₂S₂) are reported. The global minimum found on the potential energy surface of 1,2-diseleno-3,4-dithiosquaric acid presents a planar conformation. The ZZ isomer was found to have the lowest energy among the three planar conformers and the ZZ and ZE isomers are very close in energy. The optimized geometric parameters exhibit a bond length equalization relative to reference compounds, cyclobutanediselenone, and cyclobutenedithiol. The computed aromatic stabilization energy (ASE) by homodesmotic reaction (Eq 1) is −20.1 kcal/mol (MP2(fu)/6-311+G** //RHF/6-311+G**) and −14.9 kcal/mol (B3LYP//6-311+G**//B3LYP/6-311+G**). The aromaticity of 1,2-diseleno-3,4-dithiosquaric acid is indicated by the calculated diamagnetic susceptibility exaltation (Λ) −17.91 (CSGT(IGAIM)-RHF/6-311+G**//RHF/6-311+G**) and −31.01 (CSGT(IGAIM)-B3LYP/6-311+G**//B3LYP/6-311+G**). Thus, 1,2-diseleno-3,4-dithiosquaric acid fulfils the geometric, energetic and magnetic criteria of aromaticity. The calculated theoretical gas-phase acidity is ΔG^o _1(298K)=302.7 kcal/mol and ΔG^o _2(298K)=388.4 kcal/mol. Hence, 1,2-diseleno-3,4-dithiosquaric acid is a stronger acid than squaric acid(3,4-dihydroxy-3-cyclobutene-1,2-dione, H₂C₄O₄). Received: 11 April 2000 / Accepted: 7 July 2000 / Published online: 27 September 2000     

Understanding the oxidation of the tricarbon radical C3H: A reaction pathway survey

The very recent observation of molecular oxygen in interstellar space appeals for the great need of mechanistic understanding of the oxidation processes of various interstellar species. In this article, we report for the first time, the oxidation mechanism of the chainlike l‐C₃H by molecular oxygen, which is known as one of the interesting carbon‐chain hydrocarbon series C_nH detected in space. This reaction is also relevant to the combustion processes where various carbon hydrides are involved. The detailed reaction pathways were identified at the CCSD(T)/aug‐cc‐pVTZ//B3LYP/6‐311++G(d,p)+ZPVE level including various fragmentation channels. Three types of fragmentation channels are identified as the C‐transfer product P₂ (CO₂+C₂H) (?129.2kcal/mol), the C,O‐exchange product P₁ (CO+HC₂O) (?154.7kcal/mol), and the O‐transfer product P₆ (³O+HC₃O) (?44.8kcal/mol). The initially entered unstable dioxygen isomer 1a HCCCOO (?26.6 kcal/mol) would either undergo the direct O‐extrusion to give P₆ (the intrinsic barrier 7.5 kcal/mol) or take a 1,2‐O‐shift (0.8 kcal/mol barrier) to give a stable isomer 5 HCCC(O)O (?139.2kcal/mol) that can either dissociate to P₁ or to P₂. The intrinsic barrier from 5 to P₁ and P₂ is 29.1 and 23.6 kcal/mol, respectively. Clearly, the entrance thermicity 26.6 kcal/mol of 1a can sufficiently initiate the subsequent formation of all the three products. To quantitatively evaluate the kinetic competition of the three products, we performed the master equation rate constant calculations. It was shown that at 298 K, the most favorable product is P₂ (64.8%) followed by P₆ (23.6%), and P₁ (11.6%). Interestingly, at elevated temperatures, the ratio of P₆ increases with the decrease of P₂, whereas that of P₁ is little changed. Notably, the thermodynamically most stable product P₁ is kinetically the least favorable, indicative of the importance of considering the kinetics. The dominant formation of P₂ (CO₂+C₂H) shows that the important carbyne radical l‐C₃H can be effectively degraded by O₂ via the chain‐shortening step. The reactivity of the cyclic c‐C₃H radical toward O₂ is also discussed. The results are expected to enrich our understanding of the chemistry of the simplest C₃‐radical in both combustion and interstellar processes. © 2013 Wiley Periodicals, Inc.     

Theoretical study of chemosensor for fluoride anion and optical properties of the derivatives of diketopyrrolopyrrole

Spin trapping of hydroperoxyl radical (HOO^·) by the amide-linked conjugate of 5-carbamoyl-5-methyl-1-pyrroline N-oxide (AMPO) to β-cyclodextrin (β-CD) was studied computationally using a two-layered ONIOM method. From a conformational perspective, the “internal” conformation of 5R-β-CD-AMPO is more favored than the “external” conformation in which the nitrone is located outside of the cavity of the β-CD. When the HOO^· addition product is formed, the most stable isomer has the nitroxyl (N₁–O₁) moiety pointing inside the cavity of the β-CD. Thus, this “internal” conformation might protect the N₁–O₁ moiety of the resulting spin adduct from access by reducing agents, thereby improving the lifetime of the radical adduct. The computed energetic barrier for HOO^· addition to the 5R-β-CD-AMPO is 8.7?kcal/mol, which is marginally smaller than spin trapping by the non-conjugated AMPO (that is, without the β-CD). To optimize the reactivity of the β-CD-AMPO conjugate, the effect of a spacer unit between the AMPO segment and the β-CD moiety with varying methylene units, (CH₂) _n (n?=?1, 2, 3), on the energetics of HOO^· addition was evaluated. The structure with only one methylene spacer (n?=?1) appears to be optimal as determined by the smaller activation barrier (6.2?kcal/mol) for HOO^· addition to the nitrone moiety. Compared with very time-consuming quantum mechanical methods, the ONIOM method appears to offer significant advantages for evaluation of the best β-CD-AMPO conjugate for trapping of such reactive oxygen species and providing for the rational design of novel nitrones as spin traps.     

Primary steps of the mechanism of gas-phase monomolecular decomposition of nitropropenes,according to results of quantum-chemical calculations (Review)

The mechanisms of gas-phase monomolecular decomposition of cis- and trans-nitropropenes, 2-nitro-1-propene, and 2-methyl-1-nitro-1-propene were examined by DFT B3LYP/6-31G(d) calculations using GAUSSIAN’98 program package. The most probable pathway of thermal decomposition of these compounds involves formation in the primary step of four-membered cyclic intermediates, substituted oxazetes. For cis-nitropropene and 2-methyl-1-nitro-1-propene, the mechanism whose primary step is 1,5-sigmatropic hydrogen shift from the CH₃ group to the NO₂ group is principally possible.     

取代吡唑-5-酰基杂环衍生物的合成、结构与生物活性

为了寻求新的含吡唑双杂环先导化合物. 用4-取代-1-甲基-3-乙基-5-吡唑甲酰氯与2-噻唑烷酮、2-噻唑硫酮、2-噁唑烷酮等含氮杂环反应得到了12个含吡唑环的双杂环化合物. 化合物结构用IR, ¹H NMR, MS和元素分析进行了表征. 并用X射线单晶衍射法测定了化合物3-(1-甲基-3-乙基-4-硝基-5-吡唑甲酰基)-噁唑烷-2-酮(3k)的晶体结构. 晶体为单斜晶系, P2₁/n (#14)空间群, a＝1.52175(3) nm, b＝0.52970(1) nm, c＝1.58185(3) nm, β＝104.893(4), V＝1.2323(4) nm³, Z＝4, D_c＝1.45 g/cm³, F(000)＝560.00, R₁＝0.064, wR₂＝0.193. 初步生物活性实验结果表明, 在25 mg/L浓度下, 3-(1-甲基-3-乙基-4-硝基-5-吡唑甲酰基)-噻唑烷-2-酮(3c), 3-(1-甲基-3-乙基-4-硝基-5-吡唑甲酰基)-噻唑烷-2-硫酮(3g)对水稻稻瘟病菌(Pyricularia oryzae)的抑制活性达到40%. 在500 mg/L浓度下, 3-(1-甲基-3-乙基-4-溴-5-吡唑甲酰基)-噻唑烷-2-酮(3d), 3-(1-甲基-3-乙基-4-溴-5-吡唑甲酰基)-噁唑烷-2-酮(3l)对稻黑尾叶蝉(Nephotettix cinc-ticeps)的抑制活性达到53.37%.     

Structure and Stability of Isomers of the Promising Interstellar Molecule PC3O

DFT/B3LYP/6-311G(d) and CCSD(T)/6-311G(2d) single-point calculations are carried out for exploring the doublet potential energy surface (PES) of PC₃O, a molecule of potential interest in interstellar chemistry. A total of 29 minima connected by 65 interconversion transition states are located. The structures of the most relevant isomers and transition states are further optimized at the QCISD level followed by CCSD(T) single-point energy calculations. At the CCSD(T)/6-311G(2df)//QCISD/6-311G(d)+ZPVE level, the global minimum is the quasi-linear structure PCCCO 1 (0.0 kcal/mol) with a great kinetic stability of 47.9 kcal/mol, and the cumulenic form features largely in its resonance structures. Moreover, the chainlike isomer OPCCC 3 (64.5) and five-membered-ring species cPCCCO 19 (77.8) possess considerable kinetic stability of about 18.0 kcal/mol. All these three isomers are very promising candidates for future experimental and astrophysical detection. Additionally, a three-membered-ring isomer CC-cCOP 10 (69.6) has slightly lower kinetic stability of around 15 kcal/mol and may also be experimentally observable. Possible formation mechanisms of the four stable isomers in interstellar space are discussed. The present research is the first attempt to study the isomerization and dissociation mechanisms of PC _n O series. The predicted spectroscopic properties, including harmonic vibrational frequencies, dipole moments and rotational constants for the relevant isomers, are expected to be informative for the identification of PC₃O in laboratory and interstellar medium.     

Ab Initio Study on the Potential Energy Surfaces of B4 Cluster

The singlet and triplet potential energy surfaces (PES) for the isomerization and dissociation reactions of B₄ isomers have been investigated using ab initio methods. Ten B4 isomers have been identified and of these 10 species, 4 have not been reported previously. The singlet rhombic structure ¹1 is found to be the most stable on the B₄ surface, in agreement with the results of previous reports. Several isomerization and dissociation pathways have been found. On the singlet PES, the linear ¹3b can rearrange to rhombus ¹1 directly, while ¹3c rearranges to ¹1 through two‐step reactions involving a cyclic intermediate. On the triplet PES, the capped triangle structure ³2 undergoes ring opening to the linear isomer ³3b with a barrier of 34.8 kcal/mol and 44.9 kcal/mol, and the latter undergoes ring closure to the square structure ³1 with a barrier of 30.4 kcal/mol and 33.0 kcal/mol at the MP4/6–311+G(3df)//MP2/6–311G(d) and CCSD/aug‐cc‐pVTZ//MP2/6–311G(d) levels of theory, respectively. The direct decomposition of singlet B₄ yielding to B₃+B is shown to have a large endothermicity of 87.3 kcal/mol (CCSD), and that producing 2B₂ to have activation energy of 133.4 kcal/mol (CCSD).     

An ab initio study of the electronic structure of diimide

Ab initio calculations on the structure and geometry of the three isomers of N₂H₂ (trans-diimide, cis-diimide, and 1,1-dihydrodiazine) were performed both on HF and CI level using gaussian basis sets with polarization functions. The trans and cis isomers have singlet ground states; the trans isomer is found to be lower in energy than the cis isomer by 6.9 kcal/mol (HF) and 5.8 kcal/mol (CI), respectively. The barrier for the trans-cis isomerization is predicted to be 56 (HF) and 55 (CI) kcal/mol. H₂ N=N has a triplet ground state with a non-planar equilibrium geometry and a rather long NN bond of 1.34 Å. Its lowest singlet state, however, is planar with an NN double bond of 1.22 Å; it is found to lie about 3 kcal/mol above the triplet and 26 kcal/mol above the singlet ground state of trans-diimide.     

An Ab initio study on the conformations of protonated,neutral, and deprotonated amidine

Ab initio SCF molecular orbital calculations have been performed to ascertain the conformational preferences of protonated, neutral, and deprotonated amidine [HC(?NH)NH₂], using the 3-21G split valence basis set. The states of eight stable species, eight transition states, and four higher-order saddle points have been determined by complete geometry optimization utilizing analytic energy gradient techniques. Protonation at the amidine ?NH is preferred over the –NH₂ site by 37.1 kcal/mol. Neutral amidine has rotational barriers of 9.6 and 11.7 kcal/mol for the HN?CN cis and trans isomers, respectively, while all the stable HC(NH₂)₂⁺ and HC(NH)₂^? species possess torsional barriers larger than 23 kcal/mol. There is, however, essentially free C—N single-bond rotation in HC(?NH)NH₃⁺, the calculated barriers being 0.7 and 1.8 kcal/mol for the cis and trans HN?CN isomers, respectively.     

Bonding and correlation analysis of various Si2CO isomers on the potential energy surface

At various levels of theory, singlet and triplet potential energy surfaces (PESs) of Si₂CO, which has been studied using matrix isolation infrared spectroscopy, are investigated in detail. A total of 30 isomers and 38 interconversion transition states are obtained at the B3LYP/6‐311G(d) level. At the higher CCSD(T)/6‐311+G(2d)//QCISD/6‐311G(2d)+ZPVE level, the global minimum ¹1 (0.0 kcal/mol) corresponds to a three‐membered ring singlet O‐cCSiSi (¹A′). On the singlet PES, the species ¹2 (0.2 kcal/mol) is a bent SiCSiO structure with a ¹A′ electronic state, followed by a three‐membered ring isomer Si‐cCSiO (¹A′) ¹3 (23.1 kcal/mol) and a linear SiCOSi ¹4 (¹Σ⁺) (38.6 kcal/mol). The isomers ¹1, ¹2, ¹3 , and ¹4 possess not only high thermodynamic stabilities, but also high kinetic stabilities. On the triplet PES, two isomers ³1 (³B₂) (18.8 kcal/mol) and ³7 (³A″) (23.3 kcal/mol) also have high thermodynamic and kinetic stabilities. The bonding natures of the relevant species are analyzed. The similarities and differences between C₃O, C₃S, SiC₂O, and SiC₂S are discussed. The present results are also expected to be useful for understanding the initial growing step of the CO‐doped Si vaporization processes. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

The reaction of tricarbon with acetylene: an ab initio/RRKM study of the potential energy surface and product branching ratios

Ab initio calculations of the potential energy surface for the C3(1Sigmag+)+C2H2(1Sigmag+) reaction have been performed at the RCCSD(T)/cc-pVQZ//B3LYP/6-311G(d,p) + ZPE[B3LYP/6-311G(d,p)] level with extrapolation to the complete basis set limit for key intermediates and products. These calculations have been followed by statistical calculations of reaction rate constants and product branching ratios. The results show the reaction to begin with the formation of the 3-(didehydrovinylidene)cyclopropene intermediate i1 or five-member ring isomer i7 with the entrance barriers of 7.6 and 13.8 kcal/mol, respectively. i1 rearranges to the other C5H2 isomers, including ethynylpropadienylidene i2, singlet pentadiynylidene i3, pentatetraenylidene i4, ethynylcyclopropenylidene i5, and four- and five-member ring structures i6, i7, and i8 by ring-closure and ring-opening processes and hydrogen migrations. i2, i3, and i4 lose a hydrogen atom to produce the most stable linear isomer of C5H with the overall reaction endothermicity of approximately 24 kcal/mol. H elimination from i5 leads to the formation of the cyclic C5H isomer, HC2C3, +H, 27 kcal/ mol above C3+C2H2. 1,1-H2 loss from i4 results in the linear pentacarbon C5+H2 products endothermic by 4 kcal/mol. The H elimination pathways occur without exit barriers, whereas the H2 loss from i4 proceeds via a tight transition state 26.4 kcal/mol above the reactants. The characteristic energy threshold for the reaction under single collision conditions is predicted be in the range of approximately 24 kcal/mol. Product branching ratios obtained by solving kinetic equations with individual rate constants calculated using RRKM and VTST theories for collision energies between 25 and 35 kcal/mol show that l-C5H+H are the dominant reaction products, whereas HC2C3+H and l-C5+H2 are minor products with branching ratios not exceeding 2.5% and 0.7%, respectively. The ethynylcyclopropenylidene isomer i5 is calculated to be the most stable C5H2 species, more favorable than triplet pentadiynylidene i3t by approximately 2 kcal/mol.     

Isomerism in OBe3F3 + cation: anab initio study

Ab initio MP2/6-31G^*//HF/6-31G^*+ZPE(HF/6-31G^*) calculations of the potential energy surface in the vicinity of stationary points and the pathways of intramolecular rearrangements between low-lying structures of the OBe₃F₃ ⁺ cation detected in the mass spectra of μ₄-Be₄O(CF₃COO)₆ were carried out. Ten stable isomers with di- and tricoordinate oxygen atoms were localized. The relative energies of six structures lie in the range 0–8 kcal mol⁻¹ and those of the remaining four structures lie in the range 20–40 kcal mol⁻¹. Two most favorable isomers, aC _2v isomer with a dicoordinate oxygen atom, planar six-membered cycle, and one terminal fluorine atom and a pyramidalC _3v isomer with a tricoordinate oxygen atom and three bridging fluorine atoms, are almost degenerate in energy. The barriers to rearrangements with the breaking of one fluorine bridge are no higher than 4 kcal mol⁻¹, except for the pyramidalC _3v isomer (∼16 kcal mol⁻¹). On the contrary, rearrangements with the breaking of the O−Be bond occur with overcoming of a high energy barrier (∼24 kcal mol⁻¹). A planarD _3h isomer with a tricoordinate oxygen atom and linear O−Be−H fragments was found to be the most favorable for the OBe₃H₃ ⁺ cation, a hydride analog of the OBe₃F₃ ⁺ ion; the energies of the remaining five isomers are more than 25 kcal mol⁻¹ higher. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 420–430, March, 1999.     

Thermolysis of disubstituted 1,2-dioxetanes: Activation parameters and chemiexcitation yields

trans-3-Methyl-4-(p-anisyl)-1,2-dioxetane 1, trans-3-methyl-4-(o-anisyl)-1,2-dioxetane 2 , 3-methyl-3-benzyl-1,2-dioxetane 3 , and 3-methyl-3-p-methoxybenzyl-1,2-dioxetane 4 were synthesized in low yield by the β-bromo hydroperoxide method. The activation parameters were determined by the chemiluminescence method (for 1 ΔG≠ = 22.8 ± 0.3 kcal/mol, Δ≠ = 22.2, ΔS≠ = −1.7 e.u., k₆₀ = 7.6 × 10⁻³s⁻¹; for 2 ΔG≠ + 23.6 ± 0.3 kcal/mol, ΔH≠ = 22.8, ΔS≠ = −2.2 e.u., k₆₀ = 2.5 × 10⁻³S⁻¹; for 3 ΔG≠ = 24.0 ± 0.4 kcal/mol, ΔH≠ = 23.1, ΔS≠ = −2.7 e.u., k₆₀ = 1.2 × 10⁻³S⁻¹; for 4 ΔG≠ = 24.0 ± 0.2 kcal/mol, ΔH≠, = 23.2, ΔS≠, = −2.4 e.u., k₆₀ = 1.2 × 10⁻³s⁻¹). Thermolysis of 1–4 produced excited carbonyl fragments (direct production of high yields of triplets relative to excited singlets) [chemiexcitation yields ϕ^T, ϕ^S, respectively: for 1 0.02, 0.0001; for 2 0.02, 0.0001; for 3 0.03, 0.0002; for 4 0.02, 0.0001]. The effect of paramethoxyaryl substitution was consistent with electronic effects. The ortho substitution in 2 resulted in an increase in stability of the dioxetane, opposite that observed for an electronic effect. The results are discussed in relation to a diradical-like mechanism.     

Is the stereomutation of methane possible?

Large basis set ab initio calculations at correlated levels, including MP2, single reference, as well as multireference configuration interaction, carried out on the methane potential energy surface, have located and characterized a transition structure for stereomutation (one imaginary frequency). This structure is best described as a pyramidal complex between singlet methylene and a side-on hydrogen molecule with C_s symmetry. At the single reference CI level, it lies 105 kcal/mol above the methane T_d-ground state but is stable relative to dissociation into CH₂(¹A₁) and H₂ by 13 kcal/mol at 0 K (with harmonic zero point energy (ZPE) corrections for all structures). Dissociation of the transition state into triplet methylene and hydrogen also is endothermic (by 4 kcal/mol), but single bond rupture to give CH and H^. is 3 kcal/mol exothermic. Thus, it does not appear likely that methane can undergo stereomutation classically beneath the dissociation limit. Confirming earlier conclusions, side-on insertion of ¹A₁ CH₂ into H₂ in a perpendicular geometry occurs without activation energy. Planar (D_4h) methane (130.5 kcal/mol) has four imaginary frequencies. Two of these are degenerate and lead to equivalent planar C_2v structures with one three-center, two-electron bond and two two-electron bonds and two imaginary frequencies. The remaining imaginary frequencies of the D_4h form lead to tetrahedral (T_d) and pyramidal (C_4v) methane. The latter has three negative eigenvalues in the force-constant matrix; one of these leads to the T_d global minimum and the other to the C_s (parallel) stereomutation transition structure. Multireference CI calculations with a large atomic natural orbitals basis set produce similar results, with the electronic energy of the C_s stereomutation transition state 0.7 ± 0.5 kcal/mol higher than that of CH + H^. dissociation products, and a ZPE-corrected energy which is 5 ± 1 kcal/mol higher. Also considered are photochemical pathways for stereomutation and the possible effects of nuclear spin, inversion tunneling, and the parity-violating weak nuclear interaction on the possibility of an experimental detection of stereomutation in methane. © 1995 by John Wiley & Sons, Inc.     

Reaction Of 3-Nitro-1,2,4-triazolederivatives with Alkylating Agents. 1. Alkylation in the Presence of Alkali

Alkylation of 3-nitro-1,2,4-triazole and 5-methyl-3-nitro-1,2,4-triazole with dialkyl sulfates or alkyl halides in the presence of alkali proceeds with a low selectivity for the alkylating agent with the formation of two regioisomers at the N₍₁₎ and N₍₂₎ atoms of the heterocycle. Depending on the reaction conditions the proportion of the N₍₂₎ isomer was 14.6-33.8%. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 1020–1025, July, 2005.     

Theoretical study on structures and stability of HC2P isomers

 The structures and isomerization pathways of various HC₂P isomers in both singlet and triplet states are investigated at the B3LYP/6-311G(d,p), QCISD/6-311G(d,p) (for isomers only) and single-point CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p) levels. At the CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p) level, the lowest-lying isomer is a linear HCCP structure ³ 1 in the ³∑⁻ state. The second low-lying isomer has a CPC ring with exocyclic CH bonding ¹ 5 in a singlet state at 10.5 kcal/mol. The following third and fourth low-lying isomers are a singlet bent HCCP structure ¹ 1 at 20.9 kcal/mol and a bent singlet HPCC structure ¹ 3 at 35.8 kcal/mol, respectively. Investigation of the HC₂P potential-energy surface indicates that in addition to the experimentally known isomer ³ 1, the other isomers ¹ 1, ¹ 3 and ¹ 5 also have considerable kinetic stability and may thus be observable. However, the singlet and triplet bent isomers HCPC ¹ 2 and ³ 2 as well as the triplet bent isomer HPCC ³ 3 are not only high-lying but are also kinetically unstable, in sharp contrast to the situation of the analogous HCNC and HNCC species that are both kinetically stable and that have been observed experimentally. Furthermore, the reactivity of various HC₂P isomers towards oxygen atoms is briefly discussed. The results presented here may be useful for future identification of the completely unknown yet kinetically stable HC₂P isomers ¹ 1, ¹ 3 and ¹ 5 either in the laboratory or in interstellar space. Received: 5 November 2000 / Accepted: 25 November 2001 / Published online: 8 April 2002     

3,3-Sigmatropic Shifts of Allyl Group Along Cyclopentadiene Ring Perimeter

Reversible non-degenerate 3,3-sigmatropic shifts of the allyl group along the perimeter of the five-membered ring occurring with energy barriers ΔG°≠ = 28.5–30.2 kcal/mol (o-dichlorobenzene-d4) have been detected in the allyl derivatives of 5-methyl-1,2,3,4-tetramethoxycarbonylcyclopentadiene by NMR method. Using DFT B3LYP/6-311++G(d,p) method, it has been shown that degenerate migrations of the allyl group in the related 5-allyl-1,2,3,4,5-pentamethoxycarbonylcyclopentadiene should occur via 3,3-sigmatropic shift through transition states with conformation of a six-membered ring (chair or boat, with close barriers ΔG°≠ = 27.4 or 27.7 kcal/mol, respectively). The simulated higher barrier of alternative 1,5-sigmatropic shifts of the allyl group (ΔG°≠ = 30.8 kcal/mol) indicates the energy preference of the migrations via 3,3-shifts.